1. Field of the Invention
The invention is generally related to digital video transmission systems and is specifically directed to a method and apparatus for compressing and distributing digitized video over a network for supporting the transmission of live, near real-time video data.
2. Description of the Prior Art
Cameras employ digital encoders that produce industry-standard digital video streams such as, by way of example, MPEG-1 streams. The use of MPEG-1 streams is advantageous due to the low cost of the encoder hardware, and to the ubiquity of software MPEG-1 players. However, difficulties arise from the fact that the MPEG-1 format was designed primarily to support playback of recorded video from a video CD, rather than to support streaming of ‘live’ sources such as surveillance cameras and the like.
MPEG system streams contain multiplexed elementary bit streams containing compressed video and audio. Since the retrieval of video and audio data form the storage medium (or network) tends to be temporally discontinuous, it is necessary to embed certain timing information in the respective video and audio elementary streams. In the MPEG-1 standard, these consist of Presentation Timestamps (PTS) and, optionally, Decoding Timestamps (DTS).
On desktop computers, it is common practice to play MPEG-1 video and audio using a commercially available software package, such as, by way of example, the Microsoft Windows Media Player. This software program may be run as a standalone application. Otherwise, components of the player may be embedded within other software applications.
Media Player, like MPEG-1 itself, is inherently file-oriented and does support playback of continuous sources such as cameras via a network. Before Media Player begins to play back a received video file, it must first be informed of certain parameters including file name and file length. This is incompatible with the concept of a continuous streaming sources, which may not have a filename and which has no definable file length.
Moreover, the time stamping mechanism used by Media Player is fundamentally incompatible with the time stamping scheme standardized by the MPEG-1 standard. MPEG-1 calls out a time stamping mechanism which is based on a continuously incrementing 94 kHz clock located within the encoder. Moreover, the MPEG-1 standard assumes no Beginning-of-File marker, since it is intended to produce a continuous stream.
Media Player, on the other hand, accomplishes time stamping by counting 100's of nanoseconds since the beginning of the current file.